Clutched power transmitting device with reduced lag time for actuation

ABSTRACT

A power transmitting component can include a friction clutch, a ram, a pump, a fluid storage device and a valve. The ram can have a piston chamber and a piston movable therein between a first and second position to engage the friction clutch. A first inlet/outlet of the pump can be fluidly coupled to a reservoir. The fluid storage device can hold pressurized hydraulic fluid. The valve can be fluidly coupled with the piston chamber, a second inlet/outlet of the pump, and the fluid storage device. When in a first mode, the valve can permit fluid communication between the pump and the fluid storage device, inhibit fluid communication between the piston chamber and the pump, and inhibit fluid communication between the piston chamber and the fluid storage device. When in a second mode, the valve can permit fluid communication between the pump, the fluid storage device, and the piston chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. application Ser. No. 15/643,514 filed Jul. 7,2017, which is a division of U.S. application Ser. No. 14/644,314 filedMar. 11, 2015. The disclosure of each of the above-referencedapplications is incorporated by reference as if fully set forth indetail herein.

FIELD

The present disclosure relates to clutched power transmitting deviceswith reduced lag times for actuation.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Hydraulically operated clutches generally include a piston which appliesforce to the clutch system to engage a plurality of clutch plates. Inorder for the clutch plates to reach maximum separation for low dragtorque, the piston must retract a considerable distance from the pointof engagement. Typically, for the piston to move from the fullyretracted position to engage the clutch plates quickly, a high flow ofhydraulic fluid to the piston is required during this initial actuation.As the clutch plates are not engaged during this initial movement of thepiston, the fluid can be provided at a lower pressure. Once the clutchplates begin to engage, the piston has less distance to travel beforethe clutch is fully engaged, thus the high flow rate is no longerneeded. Instead, a higher pressure is required to force the clutchplates into complete engagement.

Typically, the pressure developed by a fixed displacement hydraulic pump(e.g. a gerotor pump) is directly related to the pump's input torque,and inversely related to the pump's fluid displacement, while the flowrate is directly related to the pump's fluid displacement and rotationalspeed. As a result, it can be difficult to satisfy requirements for lowpower consumption, high flow rate, and high pressure, whilesimultaneously maintaining simplicity, low cost, and robustness of afixed displacement pump.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

The present teachings provide for a power transmitting componentincluding a friction clutch, a reservoir, a hydraulic ram, a pump, afluid storage device and a first valve. The friction clutch can have aplurality of first clutch plates and a plurality of second clutch platesthat can be interleaved with the first clutch plates. The reservoir canbe configured to hold hydraulic fluid. The hydraulic ram can be coupledto the friction clutch. The hydraulic ram can have a piston chamber anda piston that can be movable in the piston chamber between a firstposition which can be retracted relative to the first and second clutchplates, and a second position in which the piston can be extended towardthe first and second clutch plates to a greater extent than when thepiston is in the first position. The pump can have a first inlet/outletand a second inlet/outlet. The first inlet/outlet can be coupled forfluid communication to the reservoir. The fluid storage device can beconfigured to hold a volume of pressurized hydraulic fluid. The firstvalve can be coupled for fluid communication with the piston chamber,the second inlet/outlet of the pump, and the fluid storage device. Thefirst valve can be operable in a first mode and a second mode. The firstvalve can be configured to permit fluid communication between the pumpand the fluid storage device, to inhibit fluid communication between thepiston chamber and the pump, and to inhibit fluid communication betweenthe piston chamber and the fluid storage device when the first valve isin the first mode. The first valve can be configured to permit fluidcommunication between the pump, the fluid storage device, and the pistonchamber when the first valve is in the second mode.

The present teachings further provide for a power transmitting componentincluding a friction clutch, a reservoir, a hydraulic ram, a pump, afluid storage device, a first valve, a second valve, and a third valve.The friction clutch can have a plurality of first clutch plates and aplurality of second clutch plates that can be interleaved with the firstclutch plates. The reservoir can be configured to hold a hydraulicfluid. The hydraulic ram can be coupled to the friction clutch. Thehydraulic ram can have a piston chamber and a piston that can be movablein the piston chamber between a first position which can be retractedrelative to the first and second clutch plates, and a second position inwhich the piston can be extended toward the first and second clutchplates to a greater extent than when the piston is in the firstposition. The pump can have a first inlet/outlet and a secondinlet/outlet. The second inlet/outlet can be coupled for fluidcommunication with the piston chamber. The pump can be operable in aforward mode and a reverse mode. In the first mode, the pump can beconfigured to pump fluid from the first inlet/outlet to the secondinlet/outlet. In the reverse mode, the pump can be configured to pumpfluid from the second inlet/outlet to the first inlet/outlet. The fluidstorage device can be configured to hold a volume of pressurizedhydraulic fluid. The first valve element can be disposed between thefluid storage device and the piston chamber. The first valve element canbe configured to permit fluid communication from the fluid storagedevice to the piston chamber. The second valve element can be disposedbetween the first inlet/outlet and the fluid storage device. The secondvalve element can be configured to permit fluid communication from thefirst inlet/outlet to the fluid storage device and can inhibit fluidcommunication from the fluid storage device to the first inlet/outlet.The third valve element can be disposed between the first inlet/outletand the reservoir. The third valve element can be configured to permitfluid communication from the reservoir to the first inlet/outlet. Thefirst, second, and third valve elements can be configured to permit thepump to pump hydraulic fluid from the reservoir to the piston chamberwhen operated in the forward mode, and can permit the pump to pumphydraulic fluid from the piston chamber to the fluid storage device whenoperated in the reverse mode.

The present teachings further provide for a power transmitting componentincluding a friction clutch, a reservoir, a hydraulic ram, a pump, afluid storage device, a first valve element, and a second valve element.The friction clutch can have a plurality of first clutch plates and aplurality of second clutch plates that can be interleaved with the firstclutch plates. The reservoir can be configured to hold a hydraulicfluid. The hydraulic ram can be coupled to the friction clutch. Thehydraulic ram can have a piston chamber and a piston that can be movablein the piston chamber between a first position which can be retractedrelative to the first and second clutch plates, and a second position inwhich the piston can be extended toward the first and second clutchplates to a greater extent than when the piston is in the firstposition. The pump can have a first inlet/outlet and a secondinlet/outlet. The first inlet/outlet can be coupled for fluidcommunication to the reservoir. The second inlet/outlet can be coupledfor fluid communication with the piston chamber. The fluid storagedevice can be configured to hold a volume of pressurized hydraulicfluid. The first valve element can be disposed between the fluid storagedevice and the piston chamber. The first valve element can be configuredto permit fluid communication from the second inlet/outlet to the fluidstorage device and to inhibit fluid communication from the fluid storagedevice to the piston chamber and the second inlet/outlet. The secondvalve element can be disposed between the fluid storage device and thepiston chamber. The second valve element can be configured to permitfluid communication from the fluid storage device to the piston chamberand to inhibit fluid communication from the piston chamber and thesecond inlet/outlet to the fluid storage device.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is an exemplary vehicle having a power transmitting componentconstructed in accordance with the present teachings;

FIG. 2 is a schematic illustration of the power transmitting componentof FIG. 1 of a first construction;

FIG. 3 is a schematic illustration of the power transmitting componentof FIG. 1 of a second construction;

FIG. 4 is a schematic illustration of the power transmitting componentof FIG. 1 of a third construction;

FIG. 5 is a schematic illustration of the power transmitting componentof FIG. 1 of a fourth construction;

FIG. 6 is a schematic illustration of the power transmitting componentof FIG. 1 of a fifth construction; and

FIG. 7 is a schematic illustration of the power transmitting componentof FIG. 1 of a sixth construction.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

With reference to FIG. 1 of the drawings, an exemplary vehicle havingclutches that can be actuated by a power transmitting componentconstructed in accordance with the teachings of the present disclosureis generally indicated by reference numeral 10. The vehicle 10 can havea power train 14 and a drive line or drive train 18. The power train 14can be conventionally constructed and can comprise a power source 22 anda transmission 26. The power source 22 can be configured to providepropulsive power and can comprise an internal combustion engine and/oran electric motor, for example. The transmission 26 can receivepropulsive power from the power source 22 and can output power to thedrive train 18. The transmission 26 can have a plurality ofautomatically or manually-selected gear ratios. The drive train 18 inthe particular example provided is of an all-wheel drive configuration,but those of skill in the art will appreciate that the teachings of thepresent disclosure are applicable to other drive train configurations,including four-wheel drive configurations, rear-wheel driveconfigurations, and front-wheel drive configurations for example.

The drive train 18 can include a front axle assembly 30, a powertake-off unit (PTU) 34, a prop shaft 38 and a rear axle assembly 42. Anoutput of the transmission 26 can be coupled to an input of the frontaxle assembly 30 to drive an input member 46 of the front axle assembly30. The PTU 34 can have a PTU input member 50, which can receive rotarypower from the input member 46 of the front axle assembly 30, and a PTUoutput member 54 that can transmit rotary power to the prop shaft 38.The prop shaft 38 can couple the PTU output member 54 to the rear axleassembly 42 such that rotary power output by the PTU 34 is received bythe rear axle assembly 42. The front axle assembly 30 and the rear axleassembly 42 could be driven on a full-time basis to drive front and rearvehicle wheels 58 and 62, respectively. It will be appreciated, however,that the drive train 18 could include one or more clutches to interruptthe transmission of rotary power through a part of the drive train 18.In the particular example provided, the drive train 18 includes a firstclutch 66, which can be configured to interrupt the transmission ofrotary power into or through the PTU 34, and a power transmittingcomponent 70, which can be configured to control rotation of componentswithin the rear axle assembly 42.

The front axle assembly 30, the PTU 34 and the first clutch 66 can bemounted in a housing assembly 74. The front axle assembly 30 can includethe input member 46, a two-speed transmission 78, a front differentialassembly 82 and a pair of front axle shafts 86. The input member 46 canbe a hollow shaft that can be configured to engage with the outputmember of the transmission 26. The input member 46 can be configured toengage with the two-speed transmission 78. The two-speed transmission 78can be configured to engage the first clutch 66 and the frontdifferential assembly 82.

The front differential assembly 82 can be coupled to the front axleshafts 86 and permit speed differentiation between the front axle shafts86. In the example provided, the front differential assembly 82 is anopen differential. It will be appreciated, however that other speeddifferentiation means could be employed in the alternative, such as oneor more clutches, a locking differential or a limited slip differentialfor example.

The PTU 34 can include the PTU input member 50, a pinion gear 90 and thePTU output member 54. The PTU input member 50 can comprise a bevel ringgear that is mounted in the housing assembly. The pinion gear 90 can bemeshingly engaged to the bevel ring gear of the PTU input member 50 andcan be aligned along an axis that is generally perpendicular to therotational axis of the input member 46. If desired, the pinion gear 90can be a hypoid pinion gear. The PTU output member 54 can be coupled tothe pinion gear 90 for rotation therewith.

The first or mode clutch 66 can be any type of clutch, including afriction clutch or a synchronizer for example. In the particular exampleprovided, the mode clutch 66 is a dog clutch having a clutch inputmember 94 and a clutch output member 98. The clutch input member 94 canbe coupled to the two-speed transmission 78 for rotation therewith. Theclutch output member 98 can be non-rotatably coupled to the bevel ringgear of the PTU input member 50. The mode clutch 66 can be operable forselectively transmitting rotary power between the clutch input member 94and the clutch output member 98.

The rear axle assembly 42 can include an input pinion 102, a bevel ringgear 106, a second differential assembly 110, a pair of second shafts114, and the power transmitting component 70. The input pinion 102 canbe coupled to an end of the propshaft 38 for rotation therewith. Thesecond bevel ring gear 106 can be meshingly engaged with the inputpinion 102. The second differential assembly 110 can be configured toreceive rotary power transmitted through the second bevel ring gear 106and to transmit that rotary power to the second shafts 114. The seconddifferential assembly 110 can have a means for permitting speeddifferentiation between the second shafts 114. In the example provided,the speed differentiation means comprises an open differential.

The power transmitting component 70 can include a second clutch 118, amotor 122, and a hydraulic system 126. The second clutch or axledisconnect clutch 118 of the power transmitting component 70 can beconfigured to selectively interrupt power transmission through thesecond differential assembly 110. The axle disconnect clutch 118 can beany type of clutch and can be mounted coaxially with the seconddifferential assembly 110. In the particular example provided, the axledisconnect clutch 118 includes a clutch input member 130, a plurality offirst clutch plates 134, a clutch output member 138, a plurality ofsecond clutch plates 142, and an actuator 146. The clutch input member130 can be coupled to the bevel ring gear 106 for rotation therewith.The plurality of first clutch plates 134 can be non-rotatably coupled tothe clutch input member 130. The clutch output member 138 can be coupledto the second differential assembly 110 to provide rotary power thereto.The plurality of second clutch plates 142 can be non-rotatably coupledto the clutch output member 138. The first and second clutch plates 134and 142 can be interleaved friction plates and the actuator 146 can beemployed to compress the first and second clutch plates 134 and 142 sothat they frictionally engage one another so that rotary power can betransmitted from the bevel ring gear 106 through the axle disconnectclutch 118 and to the second differential assembly 110. When theactuator 146 is disengaged so that rotary power is not transmittedthrough the axle disconnect clutch 118, the rear wheels 62 will drivethe second shafts 114, but the axle disconnect clutch 118 inhibits thetransmission of rotary power into the bevel ring gear 106. In this way,operation of the vehicle 10 in a front-wheel drive mode will not permitthe rear wheels 62 to “back drive” the bevel ring gear 106. In theexample provided, the motor 122 is an electric motor, though anysuitable type of motor can be used. The motor 122 can be drivinglycoupled to the hydraulic system 126 by an output shaft 150 and thehydraulic system 126 can be coupled for fluid communication with theactuator 146.

With additional reference to FIG. 2 of the drawings, the powertransmitting component 70 with the hydraulic system 126 (FIG. 1) of afirst construction is illustrated in more detail and indicated byreference number 126 a. The output shaft 150 can be rotatable in a firstdirection 210. The motor 122 can be reversible to rotate the outputshaft 150 in a second direction 214 opposite the first direction 210.The rotational direction of the motor 122 can be reversed by anysuitable means such as switching a polarity of electrical power suppliedto the motor 122, or by way of a gearbox (not shown) for example.

The actuator 146 can include a piston 218, a housing 222, and an applyplate 226. The actuator 146 can also include a return spring (notshown). The housing 222 can define a cavity 230. The piston 218 can beslidably received in the cavity 230. The piston 218 and piston cavitycan have an annular shape. The housing 222 and the piston 218 can definea piston chamber 232. The piston 218 can be coupled to the apply plate226 to translate the apply plate 226 between a first position and asecond position. In the first position, the apply plate 226 can beextended toward the first and second clutch plates 134, 142 to cause thefirst and second clutch plates 134, 142 to frictionally engage oneanother to transmit rotary power from the clutch input member 130 to theclutch output member 138. In the second position, the apply plate 226can be retracted from, or extended a lesser amount toward, the first andsecond clutch plates 134, 142. In the second position, the first andsecond clutch plates 134, 142 can be disengaged from one another so thatrotary power is not transmitted between the clutch input member 130 andthe clutch output member 138. It is understood that the actuator 146 canbe configured to be operated in any number of intermediate positionsbetween the first and second positions such that an amount of torquetransferred through the second clutch 118 can be controlled ormodulated. The return spring (not shown) can be configured to bias theapply plate 226 toward either the first or second position.

The hydraulic system 126 a can include a reservoir 238, the actuator146, a first valve 240, a pump 242, and a fluid storage device 244. Thehydraulic system 126 a can also include a second valve 246, and a thirdvalve 248. The reservoir 238 can be configured to hold a volume ofhydraulic fluid. The reservoir 238 can be fluidly coupled to the pistonchamber 232 by a bleed conduit 250. The bleed conduit 250 can beconfigured to permit a small amount of fluid to flow from the pistonchamber 232 to the reservoir 238. The bleed conduit 250 can be a smalldiameter conduit or can include a restricting element or deviceconfigured to limit the flowrate through the bleed conduit 250. Therestricting element or device can be configured to only permit fluid todrain from the piston chamber 232 to the reservoir 238 when a pressurein the piston chamber 232 exceeds a predetermined pressure.

The first valve 240 can have a plurality of inlet/outlets, including afirst port 254, a second port 256, a third port 258, and a fourth port260. The fourth port 260 can be coupled for fluid communication with thepiston chamber 232 by a first conduit 264. While schematically shown,the first valve 240 can have a valve body (not specifically shown) and avalve element (not specifically shown) that can be movable relative tothe valve body between a first position such that the first valve 240 isin a first mode (schematically shown) and a second position such thatthe first valve 240 is in a second mode (not specifically shown). Themovable element can be moved between the first and second positions(i.e. the first valve 240 can be switched between the first and secondmodes) by any suitable means, such as a solenoid 266 for example.

When the first valve 240 is in the first mode, the first valve 240 canpermit fluid communication between the first port 254 and the secondport 256. In the first mode, the first valve 240 can inhibit fluidcommunication between the third port 258 and the fourth port 260. Whilenot specifically shown, the first valve 240 can be configured to permitflow in one direction when in the first mode, such that fluid can flowfrom the first port 254 to the second port 256, while being inhibitedfrom flowing from the second port 256 to the first port 254.

When the first valve 240 is in the second mode, the first valve 240 canpermit fluid communication between the first, third, and fourth ports254, 258, 260. While not specifically shown, the first valve 240 can beconfigured to permit flow in one direction from the third port 258 whenin the second mode, such that fluid can flow from the third port 258 tothe fourth port 260, while being inhibited from flowing from the firstand fourth ports 254, 260 to the third port 258.

The pump 242 can be drivingly coupled to the output shaft 150, such thatthe motor 122 can operate the pump 242 by rotating the output shaft 150.The pump 242 can be any suitable type of pump, such as a gerotor pumpfor example. The pump 242 can be configured to be operated in a forwardmode or a reverse mode such that the pump 242 can be switched betweenthe forward and reverse modes depending on the direction of rotation ofthe output shaft 150. The pump 242 can have a plurality ofinlet/outlets, such as a fifth port 270 and a sixth port 272. The fifthport 270 can be fluidly coupled to the reservoir 238 by a second conduit274. The sixth port 272 can be fluidly coupled to the first port 254 bya third conduit 276.

The fluid storage device 244 can be a vessel defining a second chamber280 that is configured to hold a volume of pressurized hydraulic fluid.In the particular example provided, the fluid storage device 244 is anaccumulator and the second chamber 280 is partially defined by a movableelement 284 which can move to vary the volume of the second chamber 280.In the particular example provided, the fluid storage device is a springbiased accumulator, such that the movable element 284 is biased by aspring to apply pressure to fluid within the second chamber 280, thoughother types of accumulators can be used. The fluid storage device 244can have a seventh port 286 and an eighth port 288 in fluidcommunication with the second chamber 280. The seventh port 286 can becoupled for fluid communication with the second port 256 by a fourthconduit 290. The eighth port 288 can be coupled for fluid communicationwith the third port 258 by a fifth conduit 292. While not specificallyshown, the fluid storage device 244 can alternatively have a singleport, such as the seventh port 286 and not include the eighth port 288.In such a construction, the fourth and fifth conduits 290, 292 can befluidly coupled at a point between the second and third ports 256, 258and the seventh port 286.

The second valve 246 can be located fluidly in-line with the fourthconduit 290, such that the second valve 246 is located between thesecond port 256 and the seventh port 286. The second valve 246 can be aone-way valve, such as a check valve, that can permit fluid flow fromthe second port 256 to the seventh port 286, while inhibiting flow fromthe seventh port 286 to the second port 256. The third valve 248 can belocated fluidly in-line with the fifth conduit 292, such that the thirdvalve 248 is located between the third port 258 and the eighth port 288.The third valve 248 can be a one-way valve, such as a check valve, thatcan permit fluid flow from the eighth port 288 to the third port 258,while inhibiting flow from the third port 258 to the eighth port 288.

An optional second bleed conduit 296 can fluidly couple the reservoir238 and the second chamber 280. The second bleed conduit 296 can beconfigured to permit a small amount of fluid to flow from the secondchamber 280 to the reservoir 238. The second bleed conduit 296 can be asmall diameter conduit or can include a restricting element or deviceconfigured to limit the flowrate through the second bleed conduit 296.The restricting element or device can be configured to only permit fluidto drain from the second chamber 280 to the reservoir 238 when apressure in the second chamber 280 exceeds a predetermined pressure. Thesecond bleed conduit 296 can be coupled to the fourth conduit 290between the second valve 246 and the seventh port 286, or can be coupledto the fifth conduit 292 or can be directly coupled to the secondchamber 280. The second bleed conduit 296 can be coupled to the bleedconduit 250 or directly to the reservoir 238, though otherconfigurations can be used such that the second bleed conduit 296 candrain to the reservoir 238.

In operation, when the first valve 240 is in the first mode, the pump242 can be operated in the forward mode to pump fluid from the reservoir238, through the first valve 240 and into the second chamber 280. Thepump 242 can be operated in this manner for a predetermined amount oftime, until a predetermined pressure is reached within the secondchamber 280, or until fluid is needed in the piston chamber 232. If thepump 242 is shut off, fluid in the second chamber 280 can be held underpressure by the first valve 240 and/or the second valve 246. In thisway, a relatively large volume of fluid can be stored at pressure untilneeded. If the pump 242 remains on or the pressure within the secondchamber 280 exceeds a predetermined pressure, then some fluid can bedrained via the second bleed conduit 296 to maintain a desired pressure.

When engagement of the first and second clutch plates 134, 142 isdesired, the first valve 240 can switch from the first mode to thesecond mode. In the second mode, the high volume of stored fluid in thesecond chamber 280 can flow from the fluid storage device 244, throughthe first valve 240 and into the piston chamber 232 to extend the piston218 quickly toward the first and second clutch plates 134, 142. The highvolume of pressurized fluid from the second chamber 280 can move thepiston 218 more quickly than the pump 242 operating alone, which can beconfigured to operate at higher pressures and lower flowrates. With thefirst valve 240 in the second mode, the pump 242 can be operated to pumpfluid from the reservoir 238, through the first valve 240, and to thepiston chamber 232 to fully engage the first and second clutch plates134, 142. The first valve 240 and/or the third valve 248 can prevent thepump 242 from pumping fluid to the second chamber 280 when the firstvalve 240 is in the second mode. The bleed conduit 250 can permit somefluid to drain from the piston chamber 232 to the reservoir 238 tomaintain a desired pressure in the piston chamber 232. The pressurewithin the piston chamber 232 can be determined using any suitabledevice, such as a pressure sensor 294, fluidly coupled to the pistonchamber 232. The bleed conduit 250 can also permit air trapped in thehydraulic circuit 126 a to bleed to the reservoir 238. The pump 242 canalso be operated intermittently or at different speeds to modulate thepressure in the piston chamber 232 in order to modulate the torquetransferred by the clutch plates 134, 142.

When disengagement of the first and second clutch plates 134, 142 isdesired, the pump 242 can be operated in the reverse mode, with thefirst valve 240 in the second mode, to pump fluid from the pistonchamber 232 to the reservoir 238 to rapidly retract the piston 218.

With reference to FIG. 3, the power transmitting component 70 with thehydraulic system 126 (FIG. 1) of a second construction is illustratedand indicated by reference number 126 b. The hydraulic system 126 b canbe similar to the hydraulic system 126 a, except as illustrated anddescribed below. The descriptions of like numbered elements areincorporated herein by reference and will not be repeated. The hydraulicsystem 126 b can include the reservoir 238, the actuator 146, a firstvalve 310, the pump 242, and the fluid storage device 244.

The first valve 310 can have a plurality of inlet/outlets, including afirst port 318, a second port 322, and a third port 326. The third port326 can be coupled for fluid communication with the piston chamber 232by a first conduit 330. While schematically shown, first valve 310 canhave a valve body (not specifically shown) and a valve element (notspecifically shown) that can be movable relative to the valve bodybetween a first position such that the first valve 310 is in a firstmode (schematically shown) and a second position such that the firstvalve 310 is in a second mode (not specifically shown). The movableelement can be moved between the first and second positions (i.e. thefirst valve 310 can be switched between the first and second modes) byany suitable means, such as a solenoid 334 for example.

When the first valve 310 is in the first mode, the first valve 310 canpermit fluid communication between the first port 318 and the secondport 322. In the first mode, the first valve 310 can inhibit fluidcommunication between the third port 326 and the first and second ports318, 322. The first valve 310 can be configured to permit flow in onedirection when in the first mode, such that fluid can flow from thefirst port 318 to the second port 322, while being inhibited fromflowing from the second port 322 to the first port 318.

When the first valve 310 is in the second mode, the first valve 310 canpermit fluid communication between the first, second, and third ports318, 322, 326. The first valve 310 can be configured to permit flow inone direction from the second port 322 when in the second mode, suchthat fluid can flow from the second port 322 to the third port 326,while being inhibited from flowing from the first and third ports 318,326 to the second port 322.

The pump 242 can have the fifth port 270 that can be fluidly coupled tothe reservoir 238 by the second conduit 274, and the sixth port 272 thatcan be fluidly coupled to the first port 318 by the third conduit 276.The fluid storage device 244 can include the seventh port 286 and notinclude the eighth port 288 (FIG. 2) and the fifth conduit 292 (FIG. 2).The seventh port 286 can be fluidly coupled to the second port 322 bythe fourth conduit 290. The second bleed conduit 296 can be configuredas described above with reference to FIG. 2 to fluidly couple the secondchamber 280 with the reservoir 238. The second bleed conduit 296 can becoupled to the fourth conduit 290 or directly to the second chamber 280for example.

In operation, the hydraulic system 126 b can function similarly to thehydraulic system 126 a. When the first valve 310 is in the first mode,the pump 242 can be operated in the forward mode to pump fluid from thereservoir 238, through the first valve 310 and into the second chamber280. The pump 242 can be operated in this manner for a predeterminedamount of time, until a predetermined pressure is reached within thesecond chamber 280, or until fluid is needed in the piston chamber 232.If the pump 242 is shut off, fluid in the second chamber 280 can be heldunder pressure by the first valve 310. In this way, a relatively largevolume of fluid can be stored at pressure until needed. If the pump 242remains on or the pressure within the second chamber 280 exceeds apredetermined pressure, then some fluid can be drained via the secondbleed conduit 296 to maintain a desired pressure.

When engagement of the first and second clutch plates 134, 142 isdesired, the first valve 310 can switch from the first mode to thesecond mode. In the second mode, the high volume of stored fluid in thesecond chamber 280 can flow from the fluid storage device 244, throughthe first valve 310 and into the piston chamber 232 to extend the piston218 quickly toward the first and second clutch plates 134, 142. The highvolume of pressurized fluid from the second chamber 280 can move thepiston 218 more quickly than the pump 242 operating alone, which can beconfigured to operate at higher pressures and lower flowrates. With thefirst valve 310 in the second mode, the pump 242 can be operated to pumpfluid from the reservoir 238, through the first valve 310, and to thepiston chamber 232 to fully engage the first and second clutch plates134, 142. The first valve 310 can prevent the pump 242 from pumpingfluid to the second chamber 280 when the first valve 310 is in thesecond mode. The bleed conduit 250 can permit some fluid to drain fromthe piston chamber 232 to the reservoir 238 to maintain a desiredpressure in the piston chamber 232. The pressure within the pistonchamber 232 can be determined using any suitable device, such aspressure sensor 294, fluidly coupled to the piston chamber 232. Thebleed conduit 250 can also permit air trapped in the hydraulic circuit126 b to bleed to the reservoir 238. The pump 242 can also be operatedintermittently or at different speeds to modulate the pressure in thepiston chamber 232 in order to modulate the torque transferred by theclutch plates 134, 142.

When disengagement of the first and second clutch plates 134, 142 isdesired, the pump 242 can be operated in the reverse mode, with thefirst valve 310 in the second mode, to pump fluid from the pistonchamber 232 to the reservoir 238 to rapidly retract the piston 218.

With reference to FIG. 4, the power transmitting component 70 with thehydraulic system 126 (FIG. 1) of a second construction is illustratedand indicated by reference number 126 c. The hydraulic system 126 c canbe similar to the hydraulic systems 126 a and 126 b, except asillustrated and described below. The descriptions of like numberedelements are incorporated herein by reference and will not be repeated.The hydraulic system 126 c can include the reservoir 238, the actuator146, a first valve 410, a second valve 412, a third valve 414, the pump242, and the fluid storage device 244

The first valve 410 can have a plurality of inlet/outlets, including afirst port 418, and a second port 422. While schematically shown, thefirst valve 410 can have a valve body (not specifically shown) and avalve element (not specifically shown) that can be movable relative tothe valve body between a first position such that the first valve 410 isin a first mode (schematically shown) and a second position such thatthe first valve 410 is in a second mode (not specifically shown). Themovable element can be moved between the first and second positions(i.e. the first valve 410 can be switched between the first and secondmodes) by any suitable means, such as a solenoid 434 for example.

When the first valve 410 is in the first mode, the first valve 410 caninhibit fluid communication between the first port 418 and the secondport 422. When the first valve 410 is in the second mode, the firstvalve 410 can permit fluid communication between the first and secondports 418, 422. The first valve 410 can be configured to permit flow inone direction from the second port 422 when in the second mode, suchthat fluid can flow from the second port 422 to the first port 418,while being inhibited from flowing from the first port 418 to the secondport 422. The first port 418 can be fluidly coupled to the pistonchamber 232 by a first conduit 450.

The pump 242 can have the fifth port 270 that can be fluidly coupled tothe reservoir 238 by the second conduit 274, and the sixth port 272 thatcan be fluidly coupled to the piston chamber 232 by a third conduit 454.The fluid storage device 244 can include the seventh port 286 and theeighth port 288. The seventh port 286 can be fluidly coupled to thefifth port 270 by a fourth conduit 458. The eighth port 288 can befluidly coupled to the second port 422 by a fifth conduit 462.

The second valve 412 can be located fluidly in-line with the secondconduit 274, such that the second valve 412 is located between thereservoir 238 and the fifth port 270. The second valve 412 can be aone-way valve, such as a check valve, that can permit fluid flow fromthe reservoir 238 to the fifth port 270, while inhibiting flow from thefifth port 270 to the reservoir 238. The third valve 414 can be locatedfluidly in-line with the fourth conduit 458, such that the third valve414 is located between the fifth port 270 and the seventh port 286. Thethird valve 414 can be a one-way valve, such as a check valve, that canpermit fluid flow from the fifth port 270 to the seventh port 286, whileinhibiting flow from the seventh port 286 to the fifth port 270. Thefourth conduit 458 can be coupled to the second conduit 274 at alocation that is between the second valve 412 and the fifth port 270. Asecond bleed conduit 466 can also fluidly couple the second chamber 280with the reservoir 238. The second bleed conduit 466 can be configuredto permit a small amount of fluid to flow from the second chamber 280 tothe reservoir 238. The second bleed conduit 466 can be a small diameterconduit or can include a restricting element or device configured tolimit the flowrate through the second bleed conduit 466. The restrictingelement or device can be configured to only permit fluid to drain fromthe second chamber 280 to the reservoir 238 when a pressure in thesecond chamber 280 exceeds a predetermined pressure. In the exampleprovided, the second bleed conduit 466 is illustrated as coupled to thefourth conduit 458 between the third valve 414 and the seventh port 286,though other configurations can be used. For example, the second bleedconduit 466 can be alternatively coupled to the fifth conduit 462 ordirectly coupled to the second chamber 280. In the example provided, thesecond bleed conduit 466 is coupled to the bleed conduit 250, thoughother configurations can be used such that the second bleed conduit 466can drain to the reservoir 238.

In operation, when the first valve 410 is in the first mode, the pump242 can be operated in the reverse mode to pump fluid from the pistonchamber 232, through the third valve 414, and into the second chamber280. The second valve 412 can inhibit the pump 242 from pumping fluidinto the reservoir 238. The pump 242 can be operated in this manner fora predetermined amount of time, until a predetermined pressure isreached within the second chamber 280, until fluid is needed in thepiston chamber 232, or until insufficient fluid remains in the pistonchamber 232. If the pump 242 is shut off, fluid in the second chamber280 can be held under pressure by the first valve 410 and the thirdvalve 414. In this way, a relatively large volume of fluid can be storedat pressure until needed. If the pressure within the second chamber 280exceeds a predetermined pressure, then some fluid can be drained via thesecond bleed conduit 466 to maintain a desired pressure.

When engagement of the first and second clutch plates 134, 142 isdesired, the first valve 410 can switch from the first mode to thesecond mode. In the second mode, the high volume of stored fluid in thesecond chamber 280 can flow from the fluid storage device 244, throughthe first valve 410 and into the piston chamber 232 to extend the piston218 quickly toward the first and second clutch plates 134, 142. The highvolume of pressurized fluid from the second chamber 280 can move thepiston 218 more quickly than the pump 242 operating alone, which can beconfigured to operate at higher pressures and lower flowrates. With thefirst valve 410 in the first or second mode, the pump 242 can beoperated in the forward mode to pump fluid from the reservoir 238,through the third conduit 454, and to the piston chamber 232 to fullyengage the first and second clutch plates 134, 142. The first valve 410can prevent the pump 242 from pumping fluid to the second chamber 280when the first valve 240 is in the second mode, or can be switched backto the first mode to inhibit fluid communication between the first andsecond ports 418, 422. The bleed conduit 250 can permit some fluid todrain from the piston chamber 232 to the reservoir 238 to maintain adesired pressure in the piston chamber 232. The pressure within thepiston chamber 232 can be determined using any suitable device, such aspressure sensor 294, fluidly coupled to the piston chamber 232. Thebleed conduit 250 can also permit air trapped in the hydraulic circuit126 c to bleed to the reservoir 238. The pump 242 can also be operatedintermittently or at different speeds to modulate the pressure in thepiston chamber 232 in order to modulate the torque transferred by theclutch plates 134, 142.

When disengagement of the first and second clutch plates 134, 142 isdesired, the pump 242 can be operated in the reverse mode, with thefirst valve 240 in the first mode, to pump fluid from the piston chamber232 to the second chamber 280 to rapidly retract the piston 218.

With reference to FIG. 5, the power transmitting component 70 with thehydraulic system 126 (FIG. 1) of a fourth construction is illustratedand indicated by reference number 126 d. The hydraulic system 126 d canbe similar to the hydraulic system 126 c, except as illustrated anddescribed below. The descriptions of like numbered elements areincorporated herein by reference and will not be repeated. The hydraulicsystem 126 d can include the reservoir 238, the actuator 146, a firstvalve 510, the pump 242, and the fluid storage device 244.

The first valve 510 can have a plurality of inlet/outlets, including afirst port 518, a second port 522, a third port 526, and a fourth port530. While schematically shown, the first valve 510 can have a valvebody (not specifically shown) and a valve element (not specificallyshown) that can be movable relative to the valve body between a firstposition such that the first valve 510 is in a first mode (schematicallyshown) and a second position such that the first valve 510 is in asecond mode (not specifically shown). The movable element can be movedbetween the first and second positions (i.e. the first valve 510 can beswitched between the first and second modes) by any suitable means, suchas a solenoid 534 for example. The first port 518 can be coupled forfluid communication with the fifth port 270 of the pump 242 by a firstconduit 550. The second port 522 can be coupled for fluid communicationwith the reservoir 238 by a second conduit 554. The third port 526 canbe coupled for fluid communication with the seventh port 286 of thefluid storage device 244 by a third conduit 558. The fourth port 530 canbe coupled for fluid communication with the piston chamber 232 by afourth conduit 562.

When the first valve 510 is in the first mode, the first valve 510 canpermit fluid communication between the first port 518 and the third port526. In the first mode, the first valve 510 can inhibit fluidcommunication between the second port 522 and the first, third, andfourth ports 518, 526, 530. In the first mode, the first valve caninhibit fluid communication between the fourth port 530 and the first,second, and third ports 518, 522, 526. The first valve 510 can beconfigured to permit flow in one direction when in the first mode, suchthat fluid can flow from the first port 518 to the third port 526, whilebeing inhibited from flowing from the third port 526 to the first port518.

When the first valve 510 is in the second mode, the first valve 510 canpermit fluid communication between the first port 518 and the secondport 522. In the second mode, the first valve 510 can permit fluidcommunication between the third port 526 and the fourth port 530. In thesecond mode, the first valve 510 can inhibit fluid communication betweenthe first port 518 and the third and fourth ports 526, 530. In thesecond mode, the first valve 510 can inhibit fluid communication betweenthe second port 522 and the third and fourth ports 526, 530. The firstvalve 510 can be configured to permit flow in one direction from thethird port 526 when in the second mode, such that fluid can flow fromthe third port 526 to the fourth port 530, while being inhibited fromflowing from the fourth port 530 to the third port 526.

The sixth port 272 of the pump 242 can be fluidly coupled to the pistonchamber 232 by a fifth conduit 566. In the particular example shown, thefluid storage device 244 can include the seventh port 286 and notinclude the eighth port 288 (FIG. 2). The second bleed conduit 466 canbe configured as described above with reference to FIG. 2 to fluidlycouple the second chamber 280 with the reservoir 238. The second bleedconduit 466 can be coupled to the third conduit 558 or directly to thesecond chamber 280 for example.

The operation of the hydraulic system 126 d can be similar to theoperation of hydraulic system 126 c described above. When the firstvalve 510 is in the first mode, the pump 242 can be operated in thereverse mode to pump fluid from the piston chamber 232, through thefirst valve 510, and into the second chamber 280. The first valve 510can inhibit the pump 242 from pumping fluid into the reservoir 238. Thepump 242 can be operated in this manner for a predetermined amount oftime, until a predetermined pressure is reached within the secondchamber 280, until fluid is needed in the piston chamber 232, or untilinsufficient fluid remains in the piston chamber 232. If the pump 242 isshut off, fluid in the second chamber 280 can be held under pressure bythe first valve 510 in the first mode. In this way, a relatively largevolume of fluid can be stored at pressure until needed. If the pressurewithin the second chamber 280 exceeds a predetermined pressure, thensome fluid can be drained via the second bleed conduit 466 to maintain adesired pressure.

When engagement of the first and second clutch plates 134, 142 isdesired, the first valve 510 can switch from the first mode to thesecond mode. In the second mode, the high volume of stored fluid in thesecond chamber 280 can flow from the fluid storage device 244, throughthe first valve 510 and into the piston chamber 232 to extend the piston218 quickly toward the first and second clutch plates 134, 142. The highvolume of pressurized fluid from the second chamber 280 can move thepiston 218 more quickly than the pump 242 operating alone, which can beconfigured to operate at higher pressures and lower flowrates. With thefirst valve 510 in the second mode, the pump 242 can be operated in theforward mode to pump fluid from the reservoir 238, through the firstvalve 510, and to the piston chamber 232 to fully engage the first andsecond clutch plates 134, 142. The first valve 510 can prevent the pump242 from pumping fluid to the second chamber 280 when the first valve510 is in the second mode. The bleed conduit 250 can permit some fluidto drain from the piston chamber 232 to the reservoir 238 to maintain adesired pressure in the piston chamber 232. The pressure within thepiston chamber 232 can be determined using any suitable device, such aspressure sensor 294, fluidly coupled to the piston chamber 232. Thebleed conduit 250 can also permit air trapped in the hydraulic circuit126 d to bleed to the reservoir 238. The pump 242 can also be operatedintermittently or at different speeds to modulate the pressure in thepiston chamber 232 in order to modulate the torque transferred by theclutch plates 134, 142.

When disengagement of the first and second clutch plates 134, 142 isdesired, the first valve 510 can be switched back to the first mode andthe pump 242 can be operated in the reverse mode to pump fluid from thepiston chamber 232 to the second chamber 280 to rapidly retract thepiston 218. It is understood that the pump 242 can also be operated inthe reverse mode with the first valve 510 in the second mode to pumpfluid from both the piston chamber 232 and the second chamber 280 to thereservoir 238.

With reference to FIG. 6, the power transmitting component 70 with thehydraulic system 126 (FIG. 1) of a fifth construction is illustrated andindicated by reference number 126 e. The hydraulic system 126 e can besimilar to the hydraulic systems 126 a, 126 b, 126 c, and 126 d, exceptas illustrated and described below. The descriptions of like numberedelements are incorporated herein by reference and will not be repeated.The hydraulic system 126 e can include the reservoir 238, the actuator146, a first valve 610, a second valve 612, the pump 242, and the fluidstorage device 244.

The first valve 610 can have a plurality of inlet/outlets, including afirst port 618, and a second port 622. While schematically shown, firstvalve 610 can have a valve body (not specifically shown) and a valveelement (not specifically shown) that can be movable relative to thevalve body between a first position such that the first valve 610 is ina first mode (schematically shown) and a second position such that thefirst valve 610 is in a second mode (not specifically shown). Themovable element can be moved between the first and second positions(i.e. the first valve 610 can be switched between the first and secondmodes) by any suitable means, such as a solenoid 634 for example.

When the first valve 610 is in the first mode, the first valve 610 caninhibit fluid communication between the first port 618 and the secondport 622. When the first valve 610 is in the second mode, the firstvalve 610 can permit fluid communication between the first and secondports 618, 622. The first valve 610 can be configured to permit flow inone direction from the second port 622 when in the second mode, suchthat fluid can flow from the second port 622 to the first port 618,while being inhibited from flowing from the first port 618 to the secondport 622. The first port 618 can be fluidly coupled to the pistonchamber 232 by a first conduit 650.

The pump 242 can have the fifth port 270 that can be fluidly coupled tothe reservoir 238 by the second conduit 274, and the sixth port 272 thatcan be fluidly coupled to the piston chamber 232 by a third conduit 654.The fluid storage device 244 can include the seventh port 286 and theeighth port 288. The seventh port 286 can be fluidly coupled to thesixth port 272 by a fourth conduit 658. In the example provided, thefourth conduit 658 is coupled to the third conduit 654 at a locationbetween the sixth port 272 and the piston chamber 232, though otherconfigurations can be used. For example, the fourth conduit 658 canalternatively be coupled to the first conduit 650 or to the pistonchamber 232 to receive fluid from the pump 242. The eighth port 288 canbe fluidly coupled to the second port 622 by a fifth conduit 662.

The second valve 612 can be located fluidly in-line with the fourthconduit 658, such that the second valve 612 is located along the fourthconduit 658 between the sixth port 272 and the seventh port 286. Thesecond valve 612 can be a one-way valve, such as a check valve, that canpermit fluid flow from the sixth port 272 to the seventh port 286, whileinhibiting flow from the seventh port 286 to the sixth port 272. Thesecond valve 612 can have a predetermined crack pressure, such that thesecond valve 612 can inhibit fluid flow through the fourth conduit 658to the fluid storage device 244 when the pressure in the third conduit654 is below the predetermined crack pressure.

An optional second bleed conduit 296 can fluidly couple the reservoir238 and the second chamber 280. The second bleed conduit 296 can beconfigured to permit a small amount of fluid to flow from the secondchamber 280 to the reservoir 238. The second bleed conduit 296 can be asmall diameter conduit or can include a restricting element or deviceconfigured to limit the flowrate through the second bleed conduit 296.The restricting element or device can be configured to only permit fluidto drain from the second chamber 280 to the reservoir 238 when apressure in the second chamber 280 exceeds a predetermined pressure. Thesecond bleed conduit 296 can be coupled to the fourth conduit 658between the second valve 612 and the seventh port 286, or can be coupledto the fifth conduit 662 or can be directly coupled to the secondchamber 280. The second bleed conduit 296 can be coupled to the bleedconduit 250 or directly to the reservoir 238, though otherconfigurations can be used such that the second bleed conduit 296 candrain to the reservoir 238.

In operation, when the first valve 610 is in the first mode, the pump242 can be operated in the forward mode to pump fluid from the reservoir238, through the third conduit 654 and into the piston chamber 232. Thepump 242 can be operated in this manner until a predetermined pressureis reached within the piston chamber 232. Once the predeterminedpressure is exceeded, such as when the first and second clutch plates134, 142, are fully engaged and the pump 242 continues to supply fluidfor example, the second valve 612 can open to permit fluid to flow intothe second chamber 280. If the pump 242 is shut off, fluid in the secondchamber 280 can be held under pressure by the first valve 610 and thesecond valve 612. In this way, a relatively large volume of fluid can bestored at pressure until needed. If the pump 242 remains on or thepressure within the second chamber 280 exceeds a predetermined pressurefor the second chamber 280, then some fluid can be drained via thesecond bleed conduit 296 to maintain a desired pressure. Fluid can alsobe drained from the piston chamber 232 via the bleed conduit 250 tomaintain desired pressure therein. The pressure within the pistonchamber 232 can be determined using any suitable device, such aspressure sensor 294, fluidly coupled to the piston chamber 232. Thebleed conduit 250 can also permit air trapped in the hydraulic circuit126 e to bleed to the reservoir 238. The pump 242 can also be operatedintermittently or at different speeds to modulate the pressure in thepiston chamber 232 in order to modulate the torque transferred by theclutch plates 134, 142.

When disengagement of the first and second clutch plates 134, 142 isdesired, the pump 242 can be operated in the reverse mode, with thefirst valve 610 in the first mode, to pump fluid from the piston chamber232 to the reservoir 238 to rapidly retract the piston 218.

When engagement of the first and second clutch plates 134, 142 isdesired, the first valve 610 can switch from the first mode to thesecond mode. In the second mode, the high volume of stored fluid in thesecond chamber 280 can flow from the fluid storage device 244, throughthe first valve 610 and into the piston chamber 232 to extend the piston218 quickly toward the first and second clutch plates 134, 142. The highvolume of pressurized fluid from the second chamber 280 can move thepiston 218 more quickly than the pump 242 operating alone, which can beconfigured to operate at higher pressures and lower flowrates. With thefirst valve 610 in the second mode, the pump 242 can be operated to pumpfluid from the reservoir 238, through the third conduit 654, and to thepiston chamber 232 to fully engage the first and second clutch plates134, 142. The first valve 610 can prevent the pump 242 from pumpingfluid to the second chamber 280 when the first valve 610 is in the firstor second modes. The second valve 612 can prevent the pump 242 frompumping fluid to the second chamber 280 until the predetermined pressureis exceeded within the piston chamber 232 to open the second valve 612.The bleed conduit 250 can permit some fluid to drain from the pistonchamber 232 to the reservoir 238 to maintain a desired pressure in thepiston chamber 232.

With reference to FIG. 7, the power transmitting component 70 with thehydraulic system 126 (FIG. 1) of a sixth construction is illustrated andindicated by reference number 126 f. The hydraulic system 126 f can besimilar to the hydraulic system 126 e except as illustrated anddescribed below. The descriptions of like numbered elements areincorporated herein by reference and will not be repeated. The hydraulicsystem 126 f can include the reservoir 238, the actuator 146, a firstvalve 710, the pump 242, and the fluid storage device 244.

The first valve 710 can have a plurality of inlet/outlets, including afirst port 718, and a second port 722. The first port 718 can be coupledfor fluid communication with the third conduit 654 by a first conduit730, for fluid communication with the piston chamber 232. The first port718 can alternatively be coupled directly to the piston chamber 232 bythe first conduit 730. While schematically shown, the first valve 710can have a valve body (not specifically shown) and a valve element (notspecifically shown) that can be movable relative to the valve bodybetween a first position such that the first valve 710 is in a firstmode (schematically shown) and a second position such that the firstvalve 710 is in a second mode (not specifically shown). The movableelement can be moved between the first and second positions (i.e. thefirst valve 710 can be switched between the first and second modes) byany suitable means, such as a solenoid 734 for example.

In the hydraulic system 126 f, the fluid storage device 244 can includethe seventh port 286 and not include the eighth port 288 (FIG. 2) andthe fifth conduit 292 (FIG. 2). The seventh port 286 can be fluidlycoupled to the second port 722 by a fourth conduit 750. The second bleedconduit 296 can be configured as described above with reference to FIG.2 to fluidly couple the second chamber 280 with the reservoir 238. Thesecond bleed conduit 296 can be coupled to the fourth conduit 290 ordirectly to the second chamber 280 for example. The pump 242 can havethe fifth port 270 that can be fluidly coupled to the reservoir 238 bythe second conduit 274, and the sixth port 272 that can be fluidlycoupled to the first port 718 by the third conduit 654.

When the first valve 710 is in the first mode, the first valve 710 canpermit fluid communication between the first port 718 and the secondport 722. In the example illustrated, the first valve 710 can beconfigured to only permit fluid to flow in one direction through thesecond port 722 when in the first mode, such that the first valve 710can permit fluid to flow from the first port 718 to the fluid storagedevice 244 while inhibiting flow from the fluid storage device 244 tothe first port 718. In the first mode, the first valve 710 can also beconfigured such that the first valve 710 inhibits fluid flow to thefluid storage device 244 when the pressure at the first port 718 (e.g.the pressure of the piston chamber 232) is below a predeterminedpressure.

When the first valve 710 is in the second mode, the first valve 710 canpermit fluid communication between the first and second ports 718, 722.The first valve 710 can be configured to permit flow in one directionfrom the second port 722 when in the second mode, such that fluid canflow from the fluid storage device 244 to the first port 718, whilebeing inhibited from flowing from the first port 718 to the fluidstorage device 244.

In operation, the hydraulic system 126 f can operate similar to thehydraulic system 126 e. When the first valve 710 is in the first mode,the pump 242 can be operated in the forward mode to pump fluid from thereservoir 238, through the third conduit 654, and into the pistonchamber 232. The pump 242 can be operated in this manner until apredetermined pressure is reached within the piston chamber 232. Forexample, the predetermined pressure can be reached when the first andsecond clutch plates 134, 142 are fully engaged and the pump 242continues to supply fluid. Once the pressure in the piston chamber 232(or the first or third conduits 730, 654) is greater than thepredetermined pressure, the first valve 710 can permit fluid to flowthrough the second port 722 and into the second chamber 280. If the pump242 is shut off, fluid in the second chamber 280 can be held underpressure by the first valve 710. In this way, a relatively large volumeof fluid can be stored at pressure until needed. If the pump 242 remainson or the pressure within the second chamber 280 exceeds a predeterminedpressure for the second chamber 280, then some fluid can be drained viathe second bleed conduit 296 to maintain a desired pressure. Fluid canalso be drained from the piston chamber 232 via the bleed conduit 250 tomaintain desired pressure therein. The pressure within the pistonchamber 232 can be determined using any suitable device, such aspressure sensor 294, fluidly coupled to the piston chamber 232. Thebleed conduit 250 can also permit air trapped in the hydraulic system126 f to bleed to the reservoir 238. The pump 242 can also be operatedintermittently or at different speeds to modulate the pressure in thepiston chamber 232 in order to modulate the torque transferred by theclutch plates 134, 142.

When disengagement of the first and second clutch plates 134, 142 isdesired, the pump 242 can be operated in the reverse mode, with thefirst valve 710 in the first mode, to pump fluid from the piston chamber232 to the reservoir 238 to rapidly retract the piston 218.

When engagement of the first and second clutch plates 134, 142 isdesired, the first valve 710 can switch from the first mode to thesecond mode. In the second mode, the high volume of stored fluid in thesecond chamber 280 can flow from the fluid storage device 244, throughthe first valve 710 and into the piston chamber 232 to extend the piston218 quickly toward the first and second clutch plates 134, 142. The highvolume of pressurized fluid from the second chamber 280 can move thepiston 218 more quickly than the pump 242 operating alone, which can beconfigured to operate at higher pressures and lower flowrates. With thefirst valve 710 in the second mode, the pump 242 can be operated to pumpfluid from the reservoir 238, through the third conduit 654, and to thepiston chamber 232 to fully engage the first and second clutch plates134, 142. The first valve 710 can prevent the pump 242 from pumpingfluid to the second chamber 280 when the first valve 710 is in thesecond mode. The bleed conduit 250 can permit some fluid to drain fromthe piston chamber 232 to the reservoir 238 to maintain a desiredpressure in the piston chamber 232. The first valve 710 can be switchedback to the first mode and the first valve 710 can prevent the pump 242from pumping fluid to the second chamber 280 until the predeterminedpressure is exceeded within the piston chamber 232 to open the firstvalve 710 to the second port 722.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

Example embodiments are provided so that this disclosure will bethorough, and will fully convey the scope to those who are skilled inthe art. Numerous specific details are set forth such as examples ofspecific components, devices, and methods, to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to those skilled in the art that specific details need not beemployed, that example embodiments may be embodied in many differentforms and that neither should be construed to limit the scope of thedisclosure. In some example embodiments, well-known processes,well-known device structures, and well-known technologies are notdescribed in detail.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. Spatiallyrelative terms may be intended to encompass different orientations ofthe device in use or operation in addition to the orientation depictedin the figures. For example, if the device in the figures is turnedover, elements described as “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the example term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

What is claimed is:
 1. A power transmitting component comprising: afriction clutch having a plurality of first clutch plates and aplurality of second clutch plates that are interleaved with the firstclutch plates; a reservoir configured to hold a hydraulic fluid; ahydraulic ram coupled to the friction clutch, the hydraulic ram having apiston chamber and a piston that is movable in the piston chamberbetween a first position which is retracted relative to the first andsecond clutch plates, and a second position in which the piston isextended toward the first and second clutch plates to a greater extentthan when the piston is in the first position; a pump having a firstinlet/outlet and a second inlet/outlet, the first inlet/outlet coupledfor fluid communication to the reservoir, and the second inlet/outletcoupled for fluid communication with the piston chamber; a fluid storagedevice configured to hold a volume of pressurized hydraulic fluid; afirst valve element disposed between the fluid storage device and thepiston chamber, the first valve element being configured to permit fluidcommunication from the second inlet/outlet to the fluid storage deviceand to inhibit fluid communication from the fluid storage device to thepiston chamber and the second inlet/outlet; and a second valve elementdisposed between the fluid storage device and the piston chamber, thesecond valve element being configured to permit fluid communication fromthe fluid storage device to the piston chamber and to inhibit fluidcommunication from the piston chamber and the second inlet/outlet to thefluid storage device.
 2. The power transmitting component of claim 1,wherein the first valve element is configured to inhibit fluidcommunication from the second inlet/outlet to the fluid storage devicewhen a pressure of the piston chamber is less than a predeterminedpressure.
 3. The power transmitting component of claim 1, furthercomprising a bleed conduit coupled for fluid communication with thepiston chamber and the reservoir.
 4. The power transmitting component ofclaim 1, wherein the pump is operable in a forward mode and a reversemode, the pump being configured to pump hydraulic fluid from thereservoir to the piston chamber and the first valve element whenoperated in the forward mode, and being configured to pump hydraulicfluid from the piston chamber to the reservoir when operated in thereverse mode.
 5. The power transmitting component of claim 1, whereinthe fluid storage device includes a movable element, the movable elementdefining a second chamber and configured to apply pressure on hydraulicfluid within the second chamber, the second chamber being coupled forfluid communication with the first and second valve elements.
 6. Thepower transmitting component of claim 1, wherein the first and secondvalve elements are elements of a first valve, the first valve beingselectively operable in a first mode and a second mode, wherein thefirst valve element inhibits fluid communication from the fluid storagedevice to the piston chamber when in the first mode, and the secondvalve element inhibits fluid communication from the second inlet/outletto the fluid storage device when in the second mode.